Ringworm in Dogs & Cats

What is ringworm?

Ringworm is the most common fungal skin infection seen in cats. Contrary to the name, ringworm is caused by a microscopic group of parasitic fungal organisms known as dermatophytes (which means "plants that live on the skin"). Ringworm invades the dead, outer layers of the skin, claws & hair. 

Are there different types of dermatophytes?

Yes there are. In cats & dogs, there are three most common types of dermatophytes which may cause ringworm. 

Microsporum gypseum (M. gypseum)

This species of ringworm is usually from dogs and cats that dig into contaminated soil.

Microsporum canis (M. Canis) 

The source of this species of ringworm is almost always a cat & accounts for approximately 75 - 98% of ringworm seen in cats *

Trichophyton mentagrophytes

This species infects dogs and cats when they are exposed to rodents or the burrows they live in.

Microsporum canis is the most common form of ringworm in cats. It is believed that up to 20% of cats are asymptomatic carriers. This means that they carry the fungus but show no signs of infection. 

Is ringworm contagious?

Yes. Microsporum canis in particular is highly infectious. It can be passed from cat to cat, dog to cat, cat to dog, cat to human, human to cat etc. 

How does a pet become infected with ringworm?

A pet can become infected with ringworm either by direct exposure with an infected animal or via the environment, such as contaminated bedding, grooming equipment, carpet & furniture. The spores are attached to the hairs, which are shed into the environment & can remain infective for up to 13 months. 

How do I know if my pet has ringworm?

The most recognised sign your pet is infected with ringworm is circular patches of hair loss, especially around the head & limbs (although it can occur on other parts of the body also). Other signs are grey, patchy areas of baldness, with or without redness & itching, seborrhea sicca (a type of dandruff), dry/flaky skin, onychomycosis (infection of the claw & clawbed).

How is ringworm diagnosed?

1) Wood's Lamp: A simple way to diagnose ringworm is to use an ultraviolet Wood's lamp (also known as a black light) on your pet, although only around 50% of ringworm strains will show up.  The hair shafts will glow a fluorescent green when exposed to a Wood's lamp.  

2) Microscopic examination: For rapid diagnosis, your veterinarian may choose to perform a microscopic examination of the hairs for microscopic fungal pores. This method has it's pros & cons. Spores are often difficult to see, so it is best performed by an experienced mycologist (a botanist who specialises in the study of fungi). If the sample taken had no spores, diagnosis may not be accurate.

3) Culture: Your veterinarian may take some samples of your pet's hair from the infected region & growing them in a lab on a special culture which enhances fungal growth.  The benefit of performing a fungal culture is that the lab will be able to diagnose the exact species of fungus. It will take around 10 days to perform the culture. 

4) Biopsy: Sometimes if the lesions look uncharacteristic a biopsy will be performed. 

What are the treatments for ringworm?

Once your pet has been diagnosed with ringworm you will have to treat both the pet & the environment. If you live in a multiple pet household, all pets in your home will need to be treated. Carefully follow the instructions on the packet & or by your veterinarian when treating your pet. In healthy pet, ringworm will often resolve itself in 2 - 4 months. However, it is recommended you treat your pet for ringworm to speed up the process & prevent infection of humans & other pets.

Shampoos/Dips: Lime sulfur dips are the most effective. Sometimes clipping the pet (especially longhaired pets) is recommended to increase the effectiveness of treatment & also decrease environmental contamination. The pet must not be allowed to lick it's coat before it dries as this can cause vomiting. Bathing should be done every 4 - 6 days for approximately 2 - 4 weeks. Lime sulfur dips can cause yellowing of the coat, this however will fade in time.  

Griseofulvin (Fulvicin®): This is the most commonly used anti-fungal drug & the only anti-fungal drug licensed for use in the pet. Griseofulvin inhibits fungal cell wall division by altering the structure and function of the microtubules. This allows the pet's immune system to gain control & fight off the infection. 

Dosage: It comes in  tablet form given orally. Griseofulvin has to be taken twice a day, with food & it is preferable to feed a fatty meal.

Side Effects/Precautions: Griseofulvin can not be used in stud animals, pregnant animals or females you are planning to breed within 2 months of treatment, as it can cause birth defects. Side effects include nausea, fever, lethargy, diarrhoea, anaemia.  In rare cases Griseofulvin can cause  bone marrow suppression & also liver disease in pets. If your pet becomes sick seek veterinary attention immediately. Griseofulvin should not be given to cats with FIV. Pregnant women should not handle Griseofulvin.

Other drugs which may be used to treat ringworm include: Ketoconazole (Nizoral®), Itraconazole, Terbinafine - (Lamisil ®). Speak to your veterinarian for further information. 

Program® (Luthenuron): It has been suggested that has been shown to be effective against ringworm. However at the time of writing this hasn't been proven. 

Ringworm Vaccine: There is a ringworm vaccine made by Fort Dodge called Fel-O-Vax® MC-K. This vaccine must be given to health pet over 4 months of age, and is a course of 3 injections. This vaccine is only effective for M. Canis. After an initial dose is administered a second dose is given 12-16 days later. A third dose is given 26-30 days after the second dose.

Decontaminating the Environment: Vacuum daily & where possible throw out the vacuum cleaner bag. Diluted bleach (1 part bleach to 10 parts water) may be used to clean down surfaces, grooming equipment etc. Carpets & soft furnishings should be steam cleaned. Bedding & kennels will also need to be disinfected. 

Can I catch ringworm from my pet?

Yes, it is possible for humans to catch ringworm from cats & vice versa. Below is a photo of ringworm.

I would like to say a special thanks to the people who kindly submitted their ringworm photos for use with this article. Your help is greatly appreciated.

* References: Feline Husbandry of the Multi Cat Household (Niels C. Pederson)

Please note:

The medical articles on this site have not been written by a veterinarian & should not be considered a replacement for a veterinarian visit. The articles are provided for informative purposes only.

Always seek immediate veterinary advice for any problems (health or behavioral) in your pets. 

While great care has been made in the creation of these articles, we cannot guarantee the accuracy or omissions on these pages. If in any doubt whatsoever, seek professional medical advice.